Dinuclear semi-rigid Zn(salen-type) complex: role of spacer flexibility on aggregation and selectivity properties and potential application as chemosensor of ditopic amines

Recently, we have demonstrated that dinuclear Zn(salen-type) complexes having a flexible spacer, are chromogenic and fluorogenic chemosensors for biogenic amines,¹ performing as molecular tweezers toward ditopic Lewis bases in non-coordinating solvents.²,³ Considering that spacer flexibility could limit the selectivity of the chemosensor,⁴ here we present the synthesis and characterization of a new dinuclear Zn(salen-type) complex 1, having a semi-rigid spacer, in order to study the role of spacer flexibility on aggregation and selectivity properties and the potential application as chemosensors for ditopic Lewis bases. In non-coordinating solvents, the presence of a semi-rigid spacer promotes the formation of dimeric aggregates through intermolecular Zn···O interactions for dinuclear complex 1, as demonstrated by ¹H NMR and ¹H DOSY NMR spectroscopy. This is in contrast with the behaviour of dinuclear complexes containing flexible spacers, which, under the same conditions, are stable as intramolecular aggregates.²,³ This distinct aggregation mode significantly influences the sensing properties of dinuclear complex 1.